Caption: Glycine crystals. Polarised light micrograph of crystals of glycine, the simplest of the amino acids. Glycine consists of a central carbon atom, to which are attached two hydrogen atoms, one amino group and one carboxyl group. It is a neurotransmitter and important in metabolism because it contributes carbon atoms in the formation of the blood pigments. Glycine is also used in the synthesis of adenine and guanine, two of the nucleic acids, and is incorporated into protein directly. It is likely to have been the first amino acid formed on Earth at the time of the primeval soup. Magnification: x120 when printed at 10 centimetres wide.